The present invention relates generally to a powered tilt steering arrangement applicable to a vehicle steering system. The present invention relates particularly to an electrically powered tilt steering arrangement which basically enables a vehicle driver to set a steering wheel at an optimum driving position the driver desires during a reciprocatory motion thereof. Furthermore, the powered tilt steering arrangement is preferably provided with a steering wheel jump up mechanism operated upon an opening and closure of a door located at the driver's seat.
Various tilt-type steering arrangements have been developed in which the steering wheel can freely be placed at the optimum driving position that the driver desires to improve a comfortable driving of the vehicle. Almost all of such kinds of the tilt-type steering arrangements are purely mechanical and, on the other hand, automated electrical tilt-type steering arrangements are very few.
A conventional electrically powered tilt steering arrangement is exemplified by a Japanese Patent Application Unexamined Open No. Sho 59-230861 published on Dec. 25, 1984.
In the above-identified Patent Application document, a rotational movement of a motor is transmitted to a male screw to which a female screw is spirally screwed. The female screw serves to convert the rotational movement of the motor into a reciprocatory movement itself. This reciprocatory movement of the female screw permits a tilt bracket pivotally supporting the steering wheel part to be tilted through a desired angle.
Since the electrically powered tilt steering arrangement disclosed in the above-identified Japanese Patent Application document requires that the rotational movement of the motor is converted into the reciprocatory movement by means of the male and female screws, both male and female screws needs to be rotated in both normal and reverse directions. Consequently, the motor is reversible.
Therefore, such an electrical equipment as a drive circuit for driving the reversible motor in both normal and reverse directions, or switch or relay device therefor is accordingly required. In addition, the construction of the above-described powered tilt steering arrangement becomes complicated and many mechanical and electrical troubles are easy to occur. If the electrical equipment fails, the fault cannot easily be located. In this way, the arrangement has a maintenance difficulty.
In addition, since the motor is reversible and the male and female screws are spirally screwed together, abrasions of the threaded portions of both screws are unlikely as the result of a long-term operation so that a problem of durability arises. Therefore, the above-described powered tilt steering arrangement lacks practicability.
The above-described conventional electrically powered tilt steering arrangement has inherently many problems in terms of the mechanical and electrical constructions. Therefore, it is difficult to reduce such a powered tilt steering arrangement into practice.
Other conventional steering arrangements are exemplified by a Japanese Patent Application Unexamined Open No. 60-88680 published on May 18, 1985 and Japanese Patent Application Unexamined Open No. 60-157962 published on Aug. 19, 1985.
In the above-identified Japanese Patent Application documents, a so-called jump up mechanism which tilts the steering wheel toward a maximum upper limit in relation to a mounting bracket is incorporated into a manually operated or powered tilt steering arrangement in order to prevent the steering wheel from obstructing the driver's body when he leaves a driver's seat through the door with the steering wheel set at any driving position.
However, since such jump up mechanisms as disclosed in the above-identified other two Japanese Patent Application documents do not tilt the steering wheel toward the maximum upper limit instantaneously but tilt it at the same relatively slow speed as the adjustment operation of the steering wheel at the optimum driving position, it takes time and they are not suitable for the improvement in easiness of the driver's getting on and off the vehicle. In addition, readjustments of the optimum driving positions are necessary whenever the driver gets on the vehicle to drive the vehicle. In this way, the conventional tilt steering arrangements disclosed in the above-identified other two Japanese Patent Application documents also have many problems.